KCCI viewer Pat Crawford took pictures of the runner after she rescued the group with her minivan. Their bodies were covered with welts after they were hit with hailstones.

"It was unbelievable," she said. "I've never seen a human body that looked that beat up and they were still walking around," Crawford said.

Urbandale High School girls track coach Randy Hutchinson said his team runs outside in all kinds of weather, but they never go out when there are active watches or warnings.

"I've never seen it," he said. "I can't imagine golf ball or baseball-sized hail falling from the sky. That's crazy."

A severe thunderstorm warning, which includes the potential for hail, was in effect in the Grinnell area on Tuesday.

Most people don't realize how far or how fast hailstones fall.

"If you're caught outside, we see hailstones as large as baseballs traveling at 100 mph," said Polk County Emergency Manager A.J. Mumm. "Obviously, (that's) very dangerous."

He said a ditch might provide some shelter, but said that increases the danger of flash floods. He said trees aren't effective shelter because they could topple in wind and lightning.

"If people can't seek shelter, at a minimum, cover your head to provide some protection to the body," Mumm said. "The body will absorb some of the punishment, but at a minimum, try to protect the head."

Gen. David Petraeus pleaded guilty to federal charges Tuesday to end a probe into whether he provided classified information to his mistress when he was CIA director, according to a U.S. official briefed on the matter.